Marshall JTM45/100, questions, questions and more ??????

Sigs

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Currently gathering parts for a JTM45/100 JH Dickinson spec build; I have all the board parts but was wondering, is it worthwhile using any 5% CC’s in specific locations? what's the benefits ?

Did the original Marshall JTM45/100 use CC’s? If you look at the Metropoulos JTM45/100, it uses lots of CC’s.

I’m still coming to terms with what the components do on the circuit, I found this file on the Metro site, it’s for a Superlead, does anyone have anything similar for the JTM45/100? I guess there are some people on here from the Metro site.
 

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william vogel

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Carbon composition resistors are used for the cathode resistors for V1 and V2 it’s 2 820 ohm and 1 100k ohm. Make sure you get the resistors with long leads. I don’t think there were originally used for any significant purpose other than being long enough to span the distance between the turrets. I use them for this purpose. The tonestack in this particular amp is the lead type with a 33k/560pF which was changed from the original 45/100 56k/250pF. The 33k resistor could also be carbon composition. I used to have the file with all the values of everything for this amp but I deleted it. I have this exact amp right now that I built and I could save you the trouble of building it by selling it to you. Mine has Mullard mustard caps, Lemco caps and Piher resistors. It’s a NOS components build and is wonderful but too loud for me. It’s a Vox vents cabinet and uses nos preamp tubes. It’s expensive but it’s the real deal. This chassis picture, you can zoom in and look at the components to get all the correct details. This amp is make from the Dickenson amp files and I used a few more favorable brand components than what was in the Hendrix amp specifically for reliability and better looks. This is what I have.
2F8C0299-2EB0-402C-8377-11767F28A4B9.jpeg
 

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Sigs

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Thanks for the info, however the custom, import duties and shipping to the UK are extortionate, I'm building as close to original as possible.
I have all the board parts, including mustards, pihers, wima, lemcos, iskras and the filters, new Mcmurdo's , belling lee fuse holder, paxoling fuse holder, Bulgin mains, AB/CTS pots, paxolin voltage selector, a chassis, also have a set of custom trannies with Kraft/mylar and a Metro 352-114 choke due soon. Just need a paxolin impedance selector and some parts from Valvestorm and a head shell.

When installing and soldering the components, do you keep the leads straight ? or bend the ends at 90 degrees and insert into the turret ?
 

Kelia

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Carbon composition resistors are used for the cathode resistors for V1 and V2 it’s 2 820 ohm and 1 100k ohm. Make sure you get the resistors with long leads. I don’t think there were originally used for any significant purpose other than being long enough to span the distance between the turrets. I use them for this purpose. The tonestack in this particular amp is the lead type with a 33k/560pF which was changed from the original 45/100 56k/250pF. The 33k resistor could also be carbon composition. I used to have the file with all the values of everything for this amp but I deleted it. I have this exact amp right now that I built and I could save you the trouble of building it by selling it to you. Mine has Mullard mustard caps, Lemco caps and Piher resistors. It’s a NOS components build and is wonderful but too loud for me. It’s a Vox vents cabinet and uses nos preamp tubes. It’s expensive but it’s the real deal. This chassis picture, you can zoom in and look at the components to get all the correct details. This amp is make from the Dickenson amp files and I used a few more favorable brand components than what was in the Hendrix amp specifically for reliability and better looks. This is what I have.
View attachment 120499
William , could you please unsubscribe so we all stop having pain when you post pictures ! Hihi !
 
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Kelia

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Currently gathering parts for a JTM45/100 JH Dickinson spec build; I have all the board parts but was wondering, is it worthwhile using any 5% CC’s in specific locations? what's the benefits ?

Did the original Marshall JTM45/100 use CC’s? If you look at the Metropoulos JTM45/100, it uses lots of CC’s.

I’m still coming to terms with what the components do on the circuit, I found this file on the Metro site, it’s for a Superlead, does anyone have anything similar for the JTM45/100? I guess there are some people on here from the Metro site.
Following your footstep soon , I found this one last week , it's from Brian Wallace
 

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Sigs

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Could you please unsubscribe William so we all stop having pain when you post pictures ! Hihi !
I wasn't aware I was subscribed to William, how do I unsubscribe ?
 

Kelia

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I wasn't aware I was subscribed to William, how do I unsubscribe ?
That was a joke , I was asking William to unsubscribe from the forum because I love his work
and it's painful to watch and drool over it .
 

Sigs

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That was a joke , I was asking William to unsubscribe from the forum because I love his work
and it's painful to watch and drool over it .
Ok
 
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Kelia

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Carbon composition resistors are used for the cathode resistors for V1 and V2 it’s 2 820 ohm and 1 100k ohm. Make sure you get the resistors with long leads. I don’t think there were originally used for any significant purpose other than being long enough to span the distance between the turrets. I use them for this purpose. The tonestack in this particular amp is the lead type with a 33k/560pF which was changed from the original 45/100 56k/250pF. The 33k resistor could also be carbon composition. I used to have the file with all the values of everything for this amp but I deleted it. I have this exact amp right now that I built and I could save you the trouble of building it by selling it to you. Mine has Mullard mustard caps, Lemco caps and Piher resistors. It’s a NOS components build and is wonderful but too loud for me. It’s a Vox vents cabinet and uses nos preamp tubes. It’s expensive but it’s the real deal. This chassis picture, you can zoom in and look at the components to get all the correct details. This amp is make from the Dickenson amp files and I used a few more favorable brand components than what was in the Hendrix amp specifically for reliability and better looks. This is what I have.
View attachment 120499
Are those turret board from Modulus ?
 

Sigs

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The boards I have are not Modulus, unsure what William is using, you would be best to get boards and chassis from the USA, as I said before shipping from UK to Canada would be expensive.
 
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william vogel

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Are those turret board from Modulus ?
I build my own boards from sheets of G10 fiberglass phenolic that I buy 2feet x 2feet custom made. I cut it to size, drill a sometimes completely perforate on 3/8 grid depending on what year board I’m replicating. It’s time consuming but a superior product. The modulus boards are made from paper phenolic and will become conductive over time due to humidity and paper pulp absorbing the moisture. It could be 10 years before a problem if humidity is controlled but it’s not worth me taking the chance. I’ve built boards from many different phenolic materials and experienced conductivity from fairly new material that would have been avoided if I considered it forehand and I’ve concluded that it’s best to use material that’s virtually impossible for conductivity to be the best practice.
 
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_Steve

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Following your footstep soon , I found this one last week , it's from Brian Wallace
This is the schematic I built mine from. As far as I know it's the authoritive one :)

I read a detailed paper on using carbon comp resistors in audio. There was a ton of data and measurements presented. I think the takeaway was that the only positions you can really benefit from their non-linearity were plate resistors and the cathode in a cathode follower - ie places where the current is causing a large voltage swing via the resistor. However you get the additional hiss in all positions. I think the decision will be more about whether you want a super accurate clone of the original or not. I believe there are some gut shots of the Dickenson amp out there somewhere.
 

chocol8

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Exactly. You MAY get some tonal variation from a CC resistor is it is used in places with high current and large voltage swings, but not with one that is over speced.

You will get hiss, less stability, shorter life, and their values tend to drift from temperature, humidity, lead stress, and other factors. I generally minimize their use.
 

Kelia

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I build my own boards from sheets of G10 fiberglass phenolic that I buy 2feet x 2feet custom made. I cut it to size, drill a sometimes completely perforate on 3/8 grid depending on what year board I’m replicating. It’s time consuming but a superior product. The modulus boards are made from paper phenolic and will become conductive over time due to humidity and paper pulp absorbing the moisture. It could be 10 years before a problem if humidity is controlled but it’s not worth me taking the chance. I’ve built boards from many different phenolic materials and experienced conductivity from fairly new material that would have been avoided if I considered it forehand and I’ve concluded that it’s best to use material that’s virtually impossible for conductivity to be the best practice.
Thank you for this detailed post , they really look great ! Not a fan of the glow in the dark red turret boards and hope
they are a good quality product but don't really know. Oh well ! Electronics is such a beautiful science !
 

william vogel

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Thank you for this detailed post , they really look great ! Not a fan of the glow in the dark red turret boards and hope
they are a good quality product but don't really know. Oh well ! Electronics is such a beautiful science !
The Valvestorm Metro boards are also fiberglass phenolic and they are great material but I’m also not crazy about the color. If you have the capability to cut the material I can tell you where to get what I use and there’s more colors available other than the Ruby Red I prefer. I could even sell you boards but I’m not as cost effective as the other pre made stuff. The modulus boards are perfect as long as you dry them out in an oven and keep them dry.
 

chocol8

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Hoffman amps sells nice heavy duty glass eyelet and turret boards. You can get them blank, drilled, or also pre-loaded with turrets, or eyelets if you prefer.
 

william vogel

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You just have to be careful about the dimensions of materials if you’re going to make your own. The power supply board is large in early Super amplifiers.
 

Kelia

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The Valvestorm Metro boards are also fiberglass phenolic and they are great material but I’m also not crazy about the color. If you have the capability to cut the material I can tell you where to get what I use and there’s more colors available other than the Ruby Red I prefer. I could even sell you boards but I’m not as cost effective as the other pre made stuff. The modulus boards are perfect as long as you dry them out in an oven and keep them dry.
Thank you Sir , I'll send you a message this coming week.
 


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